It is well known to provide an air bag assembly including an inflatable air bag cushion for protecting the occupant of a transportation vehicle. In an automotive vehicle such air bag assemblies are typically located within the hub of the steering wheel and in a recess in the vehicle instrument panel for protection of the vehicle occupants seated in opposing relation to such assemblies. Additional air bag assemblies may be located within the seats and/or door panels for protection of the occupants during a side-impact event. It is also known to utilize inflatable curtain-like structures for deployment from the structural pillars or roof line of the motor vehicle so as to promote restraint and protection of the vehicle occupant during a roll-over event.
Air bag assemblies typically include an inflatable cushion in fluid communication with a gas emitting inflator. Upon sensing certain predetermined vehicle conditions, such as a certain level of vehicle deceleration, the inflator discharges a fixed amount of inflator gas thereby forcing the air bag into a deployed position. The inflator gas occupies the available volume within the air bag cushion thereby forcing the air bag cushion to expand outwardly to the extent permitted by its construction. The pressure within the air bag cushion upon deployment is proportional to the quantity of inflator gas expelled into the air bag and inversely proportional to the volume occupied by the inflator gas within the air bag. As the occupant comes into contact with the expanded air bag, the inflator gas is forced out of the air bag thereby dissipating the kinetic energy of the occupant achieving a so called “ride down” effect. In order to facilitate the discharge of inflator gas from the air bag it is common to incorporate vents in the form of normally open fixed diameter apertures across the walls of the air bag.
It has been recognized that in some instances it may be desirable to adjust the inflation characteristics of the air bag to reflect the nature of the impact event and/or the size and/or the position of the occupant to be protected. In order to provide a degree of control over the gas pressure within the air bag cushion it is known to use an inflator that has varied levels or stages of inflator gas output in response to the sensing of different vehicle or occupant conditions. Thus, it is generally known in the prior art to utilize so-called “dual-stage” inflators that discharge predetermined amounts of gas at different discrete levels.
In order to provide additional control over the inflation characteristics of the air bag cushion it has been suggested to utilize tethering elements in the form of straps or webs extending between surfaces of the air bag which may be released from a first restrained operative length to a second extended operative length upon the occurrence of vehicle conditions warranting an increased air bag profile. It has also been suggested to utilize air bag cushions which incorporate sewn or woven in seams within the air bag to control the expanded geometry of the inflated air bag wherein the seams separate upon the introduction of pressures exceeding a certain level thereby freeing the air bag cushion from the restraint imposed by the seams at lower pressures.